Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 250358
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1158 PM EDT Sun Jun 24 2018

.AVIATION...

Stray patches of stratocu over central Lower Michigan are associated
with cooler air moving in on northeast low level flow that is not
quite dry enough to avoid influence from Lake Huron and Saginaw Bay.
Expect these clouds to remain possible in a disorganized pattern
across SE Michigan through mid morning. Dry air then takes control
as high pressure builds over the central Great Lakes through the day
and sustains light NE wind. VFR clear ceiling and visibility will
continue through Monday evening.

.DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 327 PM EDT Sun Jun 24 2018

Showers and drizzle temporarily become better organized across
central Lower Michigan late this morning & early this afternoon as
peak heating made the most of the tail end of the existing mid and
low-level deformation axis prior to the exit of the wave to the
east. Resultant weakening of the surface trough has since supported
a reduction in coverage and intensity as it sags south, with another
flare up in coverage possible during the latter stage of peak
heating along the SW periphery of the cloud shield. Meanwhile,
ongoing cold advection will only deepen upper ridging forces high
pressure across northwest Ontario, its southern extent locally
enhanced by Lake Huron. Uncertain cloudy cover tonight will be main
concern with regard to low temperature potential. The northern
extent of the cloud shield currently extends north toward Georgian
Bay and will translate south through the CWA during the first half
of tonight. The fact that the integrity the stratus deck already
diminishes with westward extent into WI and the UP combined with
diminishing forcing overall suggests making a move toward aggressive
clearing and cooler overnight temperatures. MAV/MET blend reasonable
with temps by Monday morning ranging from the upper 40s in the Thumb
to upper 50s in the urban heat island.

High pressure will continue to migrate from northwest Ontario off
the New England coast Monday through Tuesday in response to the
closed low over Wyoming today ejecting east during this time. Solid
northeast gradient within deep tropospheric subsidence that will be
punching all the way down to the surface will ensure clear skies
save for some high cirrus encroaching from the west. Surface
temperature potential will therefore be maximized over inland areas
where 850mb temps around 10C should support highs solidly in the mid
70s with some potential for overachieving and touching 80 if cirrus
holds off. Marine layer advection will suppress mixing heights
limiting highs to the low 70s in the Thumb and Monroe County with
60s nearer the immediate shoreline. Weak gradient and clear skies
Monday night will be chilly by mid-summer standards. A simple
MAV/MET blend yields 40s north of M59, a few degrees warmer than the
1981 records of 43/44 at FNT/MBS respectively and low 40s or perhaps
upper 30s in the ag-dominated landscape of the Thumb. Return flow
emerges Tuesday as high pressure slips east supporting highs
climbing toward 80 despite a chilly start and a 10 to 15 degree
dewpoint recovery. T-storm chances ramp up beginning as early as
late Tues aftn as a deep warm frontal structure makes inroads into
Lower Michigan courtesy of a strengthening low-level jet. Some
potential for activity along the instability gradient depending on
timing, but the bulk of Tues eve/Tues night precip will likely take
the shape of elevated showers/tstorms. Early period entrance into
the warm sector will keep low temps Tues night elevated near 70
degrees.

Surface low pressure and closed upper-level low with a PV anomaly
will continue rain and thunderstorm chances across SE MI Wednesday
morning into Wednesday afternoon as decent S/SW flow allows daytime
temperatures to warm up into the low to mid-80s despite cloud cover.
Heavy downpours and lightning remain the main threat with the
precipitation as PW values range between 1.70 - 1.80 and 850 mb dew
points range between 12 - 14 C. Rain chances diminish late Wednesday
into early Thursday as the upper-level trough moves into New England

Attention will then turn to the well-above normal temperatures
forecasted for the later half of this week. Models have been
consistent with advertising temperatures that peak in the 90s for a
daytime high over the past several days. A weak cold front will keep
temperatures capped in the mid-80s for a high on Thursday, however,
850 mb temperatures are expected to soar from from an average of 15C
Thursday afternoon up to 22C by Saturday morning. Upper-level
ridging and a surface high set-up across the eastern U.S. will also
bring plenty of sunshine for the later half of the week. Strong WAA
combined with peak daytime insolation will allow daytime highs to
peak in the lower 90s on Friday, mid-90s Saturday, and lower 90s on
Sunday. Temperatures forecasted are supported by GFS and ECMWF MOS
output, both of which support highs in the mid-90s Saturday
afternoon across the Metro area and low to mid-90s across the Tri-
Cities into the Thumb. Heat advisories will likely be needed as dew
points climb into the lower-70s, making it feel like the upper-90s
to lower-100s. Isolated pop-up showers and thunderstorms are not out
of the question through the week, however, confidence is too low
regarding timing and location to highlight in the forecast.

MARINE...

Northerly flow only around 15 knots over Lake Huron will trend a bit
more easterly tomorrow as high pressure sinks into the Central Great
Lakes. Waves look to be predominately below 4 feet, and small craft
advisories have been dropped.

Winds will veer southeasterly Tuesday as a low pressure system and
attendant warm front approach the region from the upper Mississippi
River Valley. This system will bring increasing chances for showers
and thunderstorms for the midweek period.

HYDROLOGY...

Increasing chance of rain during Tuesday, with showers and
thunderstorms working through southeast Michigan Tuesday night and
Wednesday. Average rainfall around 1 inch possible, but locally
higher amounts in strong thunderstorms, which could lead to poor
drainage and urban flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
DISCUSSION...JVC/AM
MARINE.......SF
HYDROLOGY....SF


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